Computer processing and analysis of X-ray fibre diffraction data

The processing and analysis of fibre diffraction data is often cumbersome. Presented here is a compact interactive computer program, PROFIDA (processing of fibre diffraction data), for fast processing of fibre diffraction data from biological molecules without many of the difficulties. Interactive rotation and centring of the diffraction pattern allow four-quadrant averaging and background subtraction. Furthermore, film coordinates may be transformed into reciprocal-space coordinates for any orientation of the specimen. Specimen tilt towards the incident-beam direction may be determined and the appropriate correction made. In addition, a routine that scales and merges data sets from a film pack is available. Data analysis is supported by an integration routine that allows layer-line profiles to be examined and integrated and layer-line plots to be produced under control of the cursor. The program is written in C to run on the Silicon Graphics Iris workstation with a button-and-dial box using the Iris graphics library.